1. Field of the Invention
The present invention relates to the fields of DNA segments and proteins derived from bacterial species. More particularly, the invention provides Haemophilus influenzae hxuB and hxuC gene compositions and HxuB and HxuC proteins and peptides. Various methods for making and using hxuB and hxuC DNA segments and proteins are disclosed, such as, for example, the use of DNA segments as diagnostic probes and templates for protein production, and the use of DNA, proteins, peptides and antibodies in various pharmacological and immunological applications.
2. Description of the Related Art
Haemophilus influenzae type b (Hib) used to be the most frequent cause of neonatal meningitis and other invasive infections of infants and young children in the United States (Fraser et al., 1974). Children of the susceptible age range, 6 months to 4 years, generally lack antibodies to the Hib capsular polysaccharide, which is a target for antibodies protective against systemic Hib disease. Moreover, children under the age of 2 years sometimes respond poorly to currently available polysaccharide-based vaccines such as pneumococcal vaccine or the Hib vaccine. For this reason, some vaccines containing only capsular polysaccharides are of limited utility in the case of young children, the group most at risk for severe Hib infections.
Although children are sometimes poor responders to vaccines containing only capsular polysaccharides, it has been reported that children in this age group respond to protein-based immunogens (Tiller and Buckley, 1978). An efficacious vaccine against Hib was recently developed by conjugating the capsular polysaccharide from Hib to a toxoid protein and is currently being sold under the trademark HibTITER.TM. (Lederle-Praxis Biologicals). However, this vaccine is not effective against disease caused by non-typeable Haemophilus influenzae (NTHI).
NTHI strains are known to be agents of diseases such as pneumonia, bacteremia, meningitis and postpartum sepsis (Murphy et al., 1985). In particular, NTHI is a frequent etiological agent of otitis media in children and young adults, causing 20-40% of all otitis media cases. Children may experience multiple infections due to the same organism as infection generally confers no long-lasting immunity. Current therapy for chronic or repeated occurrences of otitis media includes the administration of antibiotics and the insertion of tubes to drain the inner ear. Unfortunately, at the present time, no effective vaccine is available for the treatment of these infections.
In attempts to develop vaccines that are effective against NTHI, researchers have examined the immunogenicity of other, non-capsular Hib antigens. For example, it has been reported that passive immunization with antibodies directed against non-capsular Hib antigens served to protect against experimental Hib bacteremia (Shenep et al., 1983). A number of Hib protein components have been studied as possible candidates for the production of passive or active immunoreagents. Proteins that are present at the outer membrane are more likely to be exposed, or available for antibody binding, than are more internally localized proteins. Antibodies directed against Hib outer membrane proteins have been reported to confer protection against bacteremia following intraperitoneal challenge with Hib, whereas antibodies against lipopolysaccharide components lacked protective activity (Shenep et al., 1983). However, some Hib proteins have proven to be either insufficiently antigenic, or their corresponding antibody non-protective (Granoff et al., 1986).
Certain envelope components that could be investigated as potential vaccines include the components of the macromolecular structures that interact with heme and hence allow heme uptake by H. influenzae . Elements proposed to be involved in this system to date include a periplasmic lipoprotein that binds heme and has structural similarity to an Escherichia coli dipeptide permease (Hanson and Hansen, 1991; Hanson et al., 1992) and a 39 kDa heme-binding protein reported to be present on the H. influenzae cell surface (Lee, 1992).
It is clear that while a variety of approaches to the treatment of bacterial diseases have experienced some success, the growing problems of antibiotic resistance, variability of antigens between species and in the same species through mutation of antigens, and the inefficient immune systems in young children and others, all present difficulties that need to be overcome. Thus, there exists today an immediate need for an effective treatment for all H. influenzae pathogens that can be used for a variety of infections and in all patients.